DESCRIPTION: The cloning of the ER-Beta receptor has prompted investigators to reevaluate the molecular basis for estrogen action and the role of estrogen receptors in tumors from tissues where ER-Beta is normally expressed. We hypothesize that the alterations in the amounts and/or cellular localization of ER-Beta and its splice variant isoforms are clinically important biological feature in breast cancer and other tumors (e.g. ovary, prostate). To determine if ER-Beta will be a biomarker that can provide clinicians with new prognostic and predictive information we propose the following experiments. In Phase I of this project we will prepare the molecular reagents necessary for analysis of ER-Beta in breast and other cancers and determine the protein and mRNA expression levels in normal and tumor cell lines. We will then measure the expression levels of the ER-Beta isoforms in human breast tumor samples. In Phase II of this project we will optimize conditions of current and new monoclonal antibodies for immunohistochemistry, and we will continue tumor analysis by doing a large retrospective study of patients whom received no systemic adjuvant therapy following local surgery. This type of study provides an ideal setting for evaluation of the importance of ER-Beta as a potential prognostic factor in breast cancer. PROPOSED COMMERCIAL APPLICATION: The production of monoclonal antibodies against the Estrogen Receptor Beta isoforms will provide researchers and clinicians important reagents to determine the mechanisms of action for this newly discovered receptor and its importance as a predicitive indicator in cancer. The specific isoforms that do show clinical relevance will then be used to produce a diagnostic kit so pathologists can test for ER-beta expression along with standard test for other steriod receptors (e.g. ER-alpha and Progesterone).